Elastic Modulus and Equilibrium Swelling of Poly(dimethylsiloxane) Networks

Model poly(dimethylsiloxane) (PDMS) networks and imperfect networks containing pendant chains and branched structures are prepared by end-linking mixtures of di-and monofunctional PDMS and a tetrafunctional cross-linker. Values of the equilibrium modulus of the networks, obtained from dynamic mechanical experiments, illustrate the importance of the entanglement contribution to the elastic modulus. The extents of equilibrium swelling are determined for the networks in two solvents, toluene and benzene. The predictions from the c* theorem do not apply to the model networks due to extensive interspersion of the network chains, which leads to entanglements that are not removed by swelling. The Flory-Rehner model, coupled with the phantom network model gives good agreement with swelling results when the experimentally measured elastic modulus is used in the analysis.